Mpg

[g mcmaine]

Just wondering what highway mileage you guys with stock LS swaps were getting.Thinking of putting a 5.3/4l60e into my 3.54 geared '67 c20 if mileage increase would be around 18 highway or better.Currently have 327/TH400 and trying to decide if a 700r4 behind my 327 or go to modern LS setup.Currently have a 2002 Silverado with 4.3,gets 20MPG in highway.If I can get close to that mileage, I would rather drive my '67.
Thanks,Gerald.

[Blackpony]

My truck gets around 19-20 mpg hwy. it's a 5.7 ls1 with a small cam, lightly ported heads, cai and tune. Stock intake, stock exhaust manifolds. Made 380/370 to the tires through a 4l60. Hope this helps!

[Clyde65]

I have a 4.8/4l60e, cai, headers and a performance tune, I get 19+ highway. I have gotten 20.5 once. I was driving like a granny but now I just drive normally.

[shearjs]

My 6.0/4l80e was around 14-15 with a 3.08 rear gear. Likely a lot less than that now with the 4.10 I just swapped in.

[BigRed76]

My '71 C10 has a 5.3/4L60E, 3.73's, with a CAI and headers, no tune, and gets 17-18 mpg with in town & highway driving. Haven't had it on any long trips yet.

[Billett]

My 6.0 lwb got 14 without a tune so I'm sure you can hit 20 with some decent mods and a good tune on a 5.3/4.8. I'm shooting for 18 once mines back from the shop. Look into glide driving that the eco-guys do in priuses. Its actually more efficient than driving with the proverbial eggshell under the pedal.

[g mcmaine]

Thanks for all the replies!
Gerald.

[doubeys_nova]

With 35" street friendly tires, 4.88 gears, NP208, 700R4, 4.8L, 2.5" dual exhaust, typical flowmasters and electric fan in an 85 SWB K10 I was getting 10-12 city and about 15-17 highway. IMHO 4.10/4.11 gears would do a world of difference on my fuel economy since I was running 32-3400 rpm's on the highway.

Ideally I think 24-2600 rpm's with my engine size would be pretty efficient. I read in a previous reply swapping from 3.08 w/ OD to a 4.10 hurt mileage. Bogging your engine with 3.08's down the highway plus the horrible transmission stress is not worth it. I blew my first transmission because of this.

Remember to also consider transmission gear ratios just as much your rear end ratios. .7 OD gear ratio makes a bunch of additional stress on the transmission that has to be relieved by either tire size or differential gear ratio.

When you figure gear ratio's, tire sizes and what transmission also track your multiplier on the parts it effects in front of it in the drive line.

We all want fuel efiiciency and reliability. Its just a real pain in the neck finding that balanced spot.

And for anyone that's wants to point out 4.88 gears that I have that conflicts with what I said...it is a kink I am working out. One downside to a 4x4